PURPOSE: To obtain a fuel additive concentrate for controlling an octane requirement increase in an internal combustion engine by compounding a reaction product of a polyamine and a specific acylating agent, an unhydrogenated poly-α-olefin and a mineral oil.

CONSTITUTION: A compsn. for controlling an octane requirement increase in an internal combustion engine is obtained by compounding a reaction product A of a polyamine and an acyclic hydrocarbyl substd. succinic acylating agent, an unhydrotreated poly-α-olefin having a volatility of 50% or less as determined by a predetermined method and an optional mineral oil having a viscosity index of below about 90 and a volatility of 50% or less as determined by a predetermined method. By this compsn., an octane requirement increase degree during the operation of an engine is reduced and can be made at least min.